C++可以帮我看看这个程序哪里写错了吗

char a[11], b[11];
int s1, s2, i, flag;
gets(a);
gets(b);
s1 = strlen(a);
s2 = strlen(b);
if( s1 != s2){
    printf("1\n");
}
if( s1 == s2){
    for( i = 0; i <= s1-1; i++)
    {
        if( a[i] == b[i])
        {
            continue;
        }    else if( a[i] != b[i] && abs(a[i]-b[i])==32 )
        {
            flag = 3;
        }
        else
        {
            flag = 4;
            break;
        }
    }
    if( i > s1-1 && flag != 3){
        printf("2\n");
    }
    else{
        printf("%d\n", flag);
    }
}
return 0;

}

#include<stdio.h>
#include<string.h>
#include<math.h>
int main() 
{ 
    char a[11], b[11];
    int s1, s2, i, flag=0;
    gets_s(a);
    gets_s(b);
    s1 = strlen(a);
    s2 = strlen(b);
    if (s1 != s2) {
        printf("1\n");
    }
    if (s1 == s2) {
        for (i = 0; i <= s1 - 1; i++)
        {
            if (a[i] == b[i])
            {
                continue;
            }
            else if (a[i] != b[i] && abs(a[i] - b[i]) == 32)
            {
                flag = 3;
            }
            else
            {
                flag = 4;
                break;
            }
        }
        if (i > s1 - 1 && flag != 3) {
            printf("2\n");
        }
        else {
            printf("%d\n", flag);
        }
    }
    return 0;
}

#include <stdio.h>

int main() {
    char a[11], b[11];
    int s1, s2, i, flag=2;
    gets(a);
    gets(b);
    s1 = strlen(a);
    s2 = strlen(b);
    if( s1 != s2) {
        printf("1");
    }
    if( s1 == s2) {
        for( i = 0; i <= s1 - 1; i++) {
            if( a[i] == b[i] &&flag==2) {
                continue;
            } else if( a[i] != b[i]) {
                if(abs(a[i] - b[i]) == 32) {
                    flag = 3;
                } else {
                    printf("4");
                    return 0;
                }
            }
        }
        printf("%d", flag);
    }
    return 0;
}

#include <stdio.h>
#include <string.h>

int main(void)
{
        char a[1024];
        char b[1204];
        int len_a = 0;
        int len_b = 0;
        int flag  = 0;

        printf("please input string a:");
        scanf("%s", a);
        printf("please input string b:");
        scanf("%s", b);

        len_a = strlen(a);
        len_b = strlen(b);

        if(len_a == len_b){

                if(strcmp(a, b)==0){
                        flag = 2;
                }
                else if(strcasecmp(a,b)==0){
                        flag = 3;
                }
                else{
                        flag = 4;
                }

        }
        else{
                flag = 1;
        }

        printf("the compare result is :%d\n", flag);



        return 0;
}
~